2.5 Analysis of samples
In the laboratory, palatable plant samples were dried in an oven at 80°C for 48 h and weighed. The soil samples used for measuring soil bulk density and soil water content were dried to a constant weight at 105±2℃, and the aluminum boxes with dry soil were weighed and recorded. The soil samples used for measuring organic carbon, total nitrogen, total phosphorus and total potassium concentrations were air-dried and passed through a 2-mm sieve to remove gravel and roots. The soil organic carbon and total nitrogen concentrations were measured by the K2Cr2O7-H2SO4oxidation method of Walkey and Black (Naelson and Sommers, 1982) and the Kjeldahl procedure (Foss Kieltec 8400, FOSS, DK). The soil total phosphorus and total potassium concentrations were measured by Mo-Sb colorimetry (UV-2102C, UNICO, Shanghai, China, and flame photometry, Model 2655-00 Digital Flame Analyzer, Cole-Parmer Instrument Company, Chicago, IL, USA) after the soil was digested with perchloric and nitric acid (Nelson and Sommers, 1982).
The soil bulk density and soil organic carbon and nutrient concentrations (total nitrogen, phosphorus and potassium) were used to calculate the soil organic carbon, total nitrogen, phosphorus and potassium stocks (Pang et al. 2020a, 2020b). The soil bulk density and soil water content were used to calculate the soil water storage (Jia et al., 2020). The soil water content was estimated by\(\text{SWC}=\frac{(\text{Ws}\text{Ds})}{(\text{Ws}\text{Am}})\times 100\%\), where SWC is the soil water content (%); Ws and Dsare the weight of the aluminum box with a fresh soil sample (g) and the weight of the aluminum box with a dry soil sample (g), and Am is the weight of the aluminum box (g).